Growers who lost plantings to frost may find it challenging to find a supply of transplants for replanting. In such a case, reducing plant populations will stretch out the available transplant supply. But what impact will this have on production?
There has actually been quite a bit of research in Ontario on tomato plant populations, but it was done between 1988 and 2003 on processing tomato cultivars. There was some fresh market tomato work in the mid-1990s in North Carolina. More recently, there has been some work on processing tomatoes in Ohio.
In many cases, there were no statistically significant differences in yield, maturity, or fruit size with in-row plant spacings ranging from 12” to 32” in twin rows in processing tomatoes. It’s important to note here that not all of those spacings were in the same trials.
However, certain varieties did respond to changes in plant spacing. Not surprisingly, it tended to be the early, small-vined varieties that benefited most often from closer in-row spacing. There were also a few cases in which higher populations advanced maturity or reduced fruit size slightly. See Table 1 for a summary of the Ohio and Ontario work.
Table 1: Processing tomato plant spacing research, Ohio and Ontario.
| Researchers, Location, Year | In-row spacing | Yield | Fruit size | Maturity |
| Bennett et al., Ohio, 2009 | 16”, 20”, 24”, 32” in twin rows 18” apart | No significant difference in any variety. | No significant difference for early variety. Mid-season and late variety had smaller fruit at harvest with closer spacing. | No significant difference for early and late variety. Mid-season variety had more red fruit at harvest with closer spacing. |
| Bennett et al., Ohio, 2008 | 16”, 20”, 24”, 32” in twin rows 18” apart | No significant difference in any variety. | No significant difference in any variety. | No significant difference in any variety. |
| Warner and Balkwill, Ontario, 1999-2001 | 13”, 16” in twin rows 16” or 24” apart | No significant difference except in a dry year when total and marketable yields were higher with closer spacing. | No significant difference. | No significant difference. |
| Garton, Ontario, 1994-1995 | 16”, 20” in 30” rows | No significant difference except in one year early variety had higher marketable yield with closer spacing. | No significant difference. | No significant difference except in one year early variety had less green fruit with closer spacing. |
| Garton, Ontario, 1993 | 12”, 15”, 18” in twin rows 16” apart | No significant difference. | – | – |
| Garton, Ontario, 1989-1990 | 12”, 16”, 20” in twin rows | No significant difference except in one year, mid-season variety had lower marketable yield at 20” compared to closer spacings. | – | No significant difference. |
Certainly a lot has changed, including varieties, since this work was completed. Response to lower populations will depend on variables like variety and growing conditions. However, in these trials on numerous different varieties over differing growing conditions, statistically significant responses to slight reductions in plant population were not that common.
The researchers conducting the fresh-market tomato work in North Carolina found in their work, as well as in previous studies in the literature, that as in-row spacing was wider (lower populations), fruit size and number of fruit per plant tended to increase, but early yields and total yields were likely to decrease. Early season yields could sometimes be increased by using closer in-row spacings. However, there were differences in response between cultivars.
You can read for yourself some of the Ontario research reports on plant populations in processing tomatoes in the digital archive of applied vegetable research in Ontario at ontario.ca/vegresearch.
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